1. Field of the Invention
The present invention relates to a water-in-oil emulsion containing stabilized retinol, this emulsion being particularly intended for the cosmetic and/or dermatological fields. The invention also relates to a use of this emulsion for treating the skin and to packaging which is perfectly suitable for this emulsion.
2. Discussion of the Background
Retinol is known for its beneficial effects on the skin, in particular in topical application.
Retinol has for a long time been used in the treatment of acne. However, it is in the field of repair of damage caused either by age or by over-exposure to the sun that retinol has proven to be extremely active.
Thus, the effects of retinol on cell differentiation make it possible to envisage the use thereof for, inter alia, effectively combating the appearance of wrinkles and fine lines, and for combating dryness, roughness and/or stiffness of the skin. Its activity in the regeneration of tissues makes it a very important compound in cicatrization. Repeated application of cosmetic compositions containing retinol enables, inter alia, wrinkles to be removed, the skin to be rendered smooth and small cracks in the epidermis to be repaired.
On account of these beneficial effects, it has for a very long time been sought to formulate retinol in cosmetically acceptable compositions in a form which is stable for at least several months at room temperature.
An emulsion containing retinol, which may be used in cosmetics, is described in U.S. Pat. No. 4,826,828 and WO-A-93/00085.
U.S. Pat. No. 4,826,828 pertains to a water-in-oil emulsion containing retinol, a volatile silicone and a solvent for the retinol and the volatile silicones. The preferred solvent is ethanol. However, retinol is degraded in the presence of ethanol. In order to obtain the emulsion, U.S. Pat. No. 4,826,828 teaches the preparation of a solution containing retinol being mixed, into a water-in-oil emulsion, which is to be mixed at the time of use, in order to avoid any degradation thereof. In addition, the use of an antioxidant and a metal-chelating agent in the aqueous phase is indicated as being essential.
The stability of such compositions, as indicated on the packaging of products Bioadvance and Bioadvance 2000, does not exceed one month. Thus, the stability of retinol, in compositions of this type, is insufficient for prolonged use, which makes rapid reacquisition necessary, and is therefore expensive.
WO-A-93/00085 proposes stabilization of retinol in cosmetic compositions by addition to the latter of a stabilizing complex comprising, in combination, an antioxidant and a metal ion-chelating agent. However, although the stability of the retinol appears to be enhanced in such compositions (60% of the retinol still being present in the composition after storage for three months at 40.degree. C.), the fact remains that the relative stability of the retinol is only due to the presence in the composition of a considerable amount of stabilizing antioxidants and chelating agents.
Much research has been carried out in order to minimize, or even to eliminate, the presence of such stabilizing agents in cosmetic compositions containing retinol, while at the same time retaining a stability thereof in the composition which is acceptable with regard to its effects and in relation with prolonged use of the composition.
It has been discovered, surprisingly and unexpectedly, that it is possible to formulate a water-in-oil emulsion containing retinol, that is stable with time and is intended for topical use, by appropriate selection of the various constituents of the emulsion, for the purpose of imparting specific physicochemical properties thereto.